Storage optimization manager

ABSTRACT

Techniques and mechanisms provide a storage optimization manager. Data may be optimized and maintained on various nodes in a cluster. Particular nodes may be overburdened while other nodes remain relatively unused. Techniques are provided to efficiently optimize data onto nodes to enhance operational efficiency. Data access requests for optimized data are monitored and managed to allow for intelligent maintenance of optimized data.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application No. 61/389,602 filed Oct. 4, 2010 and titled “DATA BLOCK MIGRATION,” the entirety of which is incorporated by reference for all purposes.

DESCRIPTION OF RELATED ART

Maintaining vast amounts of data is resource intensive not just in terms of the physical hardware costs but also in terms of system administration and infrastructure costs. Some mechanisms provide compression of data to save resources. For example, some file formats such as the Portable Document Format (PDF) are compressed. Some other utilities allow compression on an individual file level in a relatively inefficient manner.

Data deduplication refers to the ability of a system to eliminate data duplication across files to increase storage, transmission, and/or processing efficiency. A storage system which incorporates deduplication technology involves storing a single instance of a data segment that is common across multiple files. In some examples, data sent to a storage system is segmented in fixed or variable sized segments. Each segment is provided with a segment identifier (ID), such as a digital signature or a hash of the actual data. Once the segment ID is generated, it can be used to determine if the data segment already exists in the system. If the data segment does exist, it need not be stored again.

In many conventional implementations, data blocks are maintained in a variety of nodes in a cluster. However, mechanisms managing node usage are limited. Consequently, mechanisms are provided for improving the management of storage optimization.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may best be understood by reference to the following description taken in conjunction with the accompanying drawings, which illustrate particular embodiments of the present invention.

FIG. 1 illustrates a particular example of a system that can use the techniques and mechanisms of the present invention.

FIG. 2 illustrates one example of a locker.

FIG. 3A illustrates one example of monitoring data access.

FIG. 3B illustrates one example of redistributing optimized data.

FIG. 4A illustrates a particular example of a filemap.

FIG. 4B illustrates a particular example of a datastore suitcase.

FIG. 5 illustrates a particular example of a deduplication dictionary.

FIG. 6A illustrates a particular example of a file having a single data segment.

FIG. 6B illustrates a particular example of a file having multiple data segments and components.

FIG. 7 illustrates a particular example of a computer system.

DESCRIPTION OF PARTICULAR EMBODIMENTS

Reference will now be made in detail to some specific examples of the invention including the best modes contemplated by the inventors for carrying out the invention. Examples of these specific embodiments are illustrated in the accompanying drawings. While the invention is described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the invention to the described embodiments. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

For example, the techniques and mechanisms of the present invention will be described in the context of data blocks. However, it should be noted that the techniques and mechanisms of the present invention apply to a variety of different data constructs including variations to data blocks. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. Particular example embodiments of the present invention may be implemented without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.

Various techniques and mechanisms of the present invention will sometimes be described in singular form for clarity. However, it should be noted that some embodiments include multiple iterations of a technique or multiple instantiations of a mechanism unless noted otherwise. For example, a system uses a processor in a variety of contexts. However, it will be appreciated that a system can use multiple processors while remaining within the scope of the present invention unless otherwise noted. Furthermore, the techniques and mechanisms of the present invention will sometimes describe a connection between two entities. It should be noted that a connection between two entities does not necessarily mean a direct, unimpeded connection, as a variety of other entities may reside between the two entities. For example, a processor may be connected to memory, but it will be appreciated that a variety of bridges and controllers may reside between the processor and memory. Consequently, a connection does not necessarily mean a direct, unimpeded connection unless otherwise noted.

Overview

Techniques and mechanisms provide a storage optimization manager. Data may be optimized and maintained on various nodes in a cluster. Particular nodes may be overburdened while other nodes remain relatively unused. Techniques are provided to efficiently optimize data onto nodes to enhance operational efficiency. Data access requests for optimized data are monitored and managed to allow for intelligent maintenance of optimized data.

EXAMPLE EMBODIMENTS

Maintaining, managing, transmitting, and/or processing large amounts of data can have significant costs. These costs include not only power and cooling costs but system maintenance, network bandwidth, and hardware costs as well.

Some efforts have been made to reduce the footprint of data maintained by file servers and reduce the associated network traffic. A variety of utilities compress files on an individual basis prior to writing data to file servers. Compression algorithms are well developed and widely available. Some compression algorithms target specific types of data or specific types of files. Compression algorithms operate in a variety of manners, but many compression algorithms analyze data to determine source sequences in data that can be mapped to shorter code words. In many implementations, the most frequent source sequences or the most frequent long source sequences are replaced with the shortest possible code words.

Data deduplication reduces storage footprints by reducing the amount of redundant data. Deduplication may involve identifying variable or fixed sized segments. According to various embodiments, each segment of data is processed using a hash algorithm such as MD5 or SHA-1. This process generates a unique ID, hash, or reference for each segment. That is, if only a few bytes of a document or presentation are changed, only changed portions are saved. In some instances, a deduplication system searches for matching sequences using a fixed or sliding window and uses references to identify matching sequences instead of storing the matching sequences again.

In a data deduplication system, the backup server working in conjunction with a backup agent identifies candidate files for backup, creates a backup stream and sends the data to the deduplication system. A typical target system in a deduplication system will deduplicate data as data segments are received. A block that has a duplicate already stored on the deduplication system will not need to be stored again. However, other information such as references and reference counts may need to be updated. Some implementations allow the candidate data to be directly moved to the deduplication system without using backup software by exposing a NAS drive that a user can manipulate to backup and archive files.

In an active file system, nodes may need to be added or removed during system operation. It is often desirable to be able to migrate data blocks around the cluster in the face of node addition and node deletion. According to various embodiments, each block map and datastore suitcase in a cluster has a suitcase ID or SCID. An SCID identifies the node and the block map or datastore suitcase, so an SCID can globally identify a file located within the cluster.

According to various embodiments, the techniques and mechanisms of the present invention allow for mapping of nodes to an SCID in light of node addition and deletion. Node mappings can be changed while limiting or avoiding data copying. In particular embodiments, each SCID need not be scanned to update each blockmap to modify the SCID. The techniques of the present invention can be applied to any clustered environment with any number of nodes. Data can be rebalanced across the nodes whenever a new node is added. Similarly, data can be redistributed from a node when that node scheduled for removal while copying only data from the node to be removed.

Many existing mapping functions have a number of drawbacks. Many mapping functions can be difficult to calculate and may require numerous processor cycles. The mapping functions may require that keys be rewritten whenever a mapping function changes and may require extra copying of data between existing members when a new node is added. When adding a new node to a two node cluster, a less efficient solution may require copying data to the new node along with copying data from node 1 to node 2 and from node 2 to node 1. According to various embodiments of the present invention, data is only copied to the new node.

According to various embodiments, a node number can be obtained from a SCID using a function such as #define get_the_node_number_from_the_scid(_scid_)\scid_to_node_array[_scid_% MAX_CLUSTER_SIZE]. A mapping function allows a key to identify the node that holds the data. According to various embodiments, the mapping function can be changed while new keys are being generated. The keys themselves may contain a node number so that keys can be allocated independently on each node without communicating between the nodes. In particular embodiments, existing keys need not be rewritten to relocate data blocks to different nodes during a node addition or deletion. When a node is added, an arbitrary amount of data can be copied from each node to the new node to rebalance the data across the cluster.

FIG. 1 shows a multi-tenant on demand infrastructure. Multiple virtual machines including virtual machines corresponding to virtual images 101, 103, 105, 107, and 109 are running on a multiple processor core shared server platform 141. According to various embodiments, virtual image A 101 is running a server operating system, a database server, as well as one or more custom applications. Virtual images 103 and 105 are clones of virtual image A 101. According to various embodiments, virtual image B 107 is running a server operating system, a database server, a web server, and/or one or more custom applications. Virtual image 109 is a clone of virtual image B 107. In particular embodiments, a user 111 is connected to a virtual image A 101. Users 113, 115, and 117 are connected to virtual image A clone 103. Users 119 and 121 are connected to virtual image A clone 105. Users 123, 125, and 127 are connected to virtual image B 107. Users 129 and 131 are connected to virtual image B clone 109.

A compute cloud service provider allows a user to create new instances of virtual images on demand. These new instances may be clones of exiting virtual machine images. An object optimization system provides application program interfaces (APIs) which can be used to instantly clone a file. When the API is used, a new stub is put in the user namespace and a block map file is cloned.

In particular embodiments, every file maintained in an object optimization system is represented by a block map file that represents all objects found in that file. The block map file includes the offsets and sizes of each object. Each entry in a block map file then points to a certain offset within a data suitcase. According to various embodiments, many block map files will be pointing to fewer data suitcases, hence resulting in multiple files sharing the same data blocks.

According to various embodiments, the block map file maintains all of the same offsets and location pointers as the original file's block map, so no user file data need be copied. In particular embodiments, if the cloned file is later modified, the behavior is the same as what happens when a deduplicated file is modified.

FIG. 2 illustrates one example of an optimized file structure. According to various embodiments, an optimization system is told where it will store its data structures, where the data input stream is coming from, what the scope of optimization is, which optimization actions to apply to the stream, and how to mark data as having been optimized. Data is then optimized. In particular embodiments, optimized data is stored in a locker 221. The locker 221 can be a directory, a volume, a partition, or an interface to persistent object storage. Within that locker 221, optimized data is stored in containers or structures such as suitcase 271. In a file system, each suitcase 271 could be a file. In block or object storage, other formats may be used. A user viewable namespace 201 includes multiple stub files 211. According to various embodiments, stub files 211 correspond to virtual image A 213 and virtual image B 215. Virtual image A 213 is associated with extended attribute information 217 including file size data and/or other metadata. Virtual image B 215 is associated with extended attribute information 219 including file size data and/or other metadata.

According to various embodiments, optimized data is maintained in a locker 221. Block map files 261 include offset, length, and location identifiers for locating appropriate data segments in a datastore suitcase 271. Multiple block map files may point to the same data segments in a data store suitcase. Each blockmap file also has corresponding extended attribute information 231 and 241 corresponding to directory handle virtual image A 233 and directory handle virtual image B 243.

FIG. 3A illustrates one example of a technique for monitoring data access. At 311, a stub file access is detected. The stub file corresponds to a virtual image of an optimized file and includes extended attribute information such as metadata. According to various embodiments, the stub file provides a suitcase identifier (SCID). In particular embodiments, the suitcase identifier specifies a node. In particular embodiments, extended attribute information and metadata can be accessed immediately in a user space. At 313, access of extended attribute information and metadata is detected. At 315, the node specified by the SCID is determined. According to various embodiments, a node specified by the SCID is determined. In particular embodiments, the node number is identified by accessing an index using the modulo of the SCID and the max cluster size. In some examples, the node number is obtained from an SCID using a function such as the following:

-   -   #define get_the_note_number_from_the_scid(_scid_)         -   scid_to_node_array[_scid_% MAX_CLUSTER_SIZE]

At 317, information about access of the particular node is maintained. According to various embodiments, the user may access a blockmap file coresponding to the node. The blockmap file includes offset, length, and location information identifying data segments in a data store suitcase. According to various embodiments, the blockmap file need not be accessed, scanned, or updated upon data migration. At 319, the data store suitcase in the appropriate node is accessed. At 321, metadata in the datastore suitcase may be obtained. At 323, data segments in the datastore suitcase may be obtained. The data segments may be reflated and/or decompressed at 325 to obtained unoptimized data.

FIG. 3B illustrates one example of a technique for redistributing data. Although the technique will be described in the context of data redistribution, it should be recognized that various techniques can also apply to redistribution upon node removal or addition. At 331, data access is monitored. According to various embodiments, data access may be disproportionately concentrated in one particular node. In particular embodiments, it may be desirable to distribute data access requests across multiple nodes so that data access efficiency can be improved. In other examples, it may be beneficial to redistribute optimized data based on node performance characteristics of location. In particular embodiments, more frequently accessed and critical data is redistributed onto nodes having higher performance capabilities.

A data imbalance is detected at 333. A data imbalance may require a simple redistribution of data or may entail addition or removal of nodes. In particular embodiments, metrics are analyzed to determine how to efficiently distribute optimized data across multiple nodes at 335. Metrics may include frequency of access, location of access, number of segments accessed in a particular period of time, network bandwidth usage, access times, latency, criticality, etc. According to various embodiments, a multicluster system may determine that particular nodes are heavily used while others remain sparsely used. In other examples, a system may detect that additional nodes are needed based on storage usage. In other examples, a node may be added or deleted even without any determination of data imbalance. Adding a node may correspond to bringing additional storage arrays or storage devices online in a storage cluster.

At 337, multiple keys are generated. In particular embodiments, a mapping function is rewritten at 339. In particular embodiments, the multiple keys may be suitcase identifiers and/or correspond to particular blockmap files. According to various embodiments, the mapping function provides that the keys identify or correspond to particular nodes. The mapping function may be rewritten while generating the multiple keys. At 341, data is redistributed across multiple nodes to rebalance data across the data storage cluster. According to various embodiments, blockmap files need not be scanned, accessed, analyzed, or modified during redistribution, node addition, removal, or modification. In particular embodiments, blockmap files remain unchanged.

FIG. 4A illustrates one example of a block map file or filemap and FIG. 4B illustrates a corresponding datastore suitcase created after optimizing a file X. Filemap file X 401 includes offset 403, index 405, and lname 407 fields. According to various embodiments, each segment in the filemap for file X is 8K in size. In particular embodiments, each data segment has an index of format <Datastore Suitcase ID>. <Data Table Index>. For example, 0.1 corresponds to suitcase ID 0 and datatable index 1. while 2.3 corresponds to suitcase ID 2 and database index 3. The segments corresponding to offsets 0K, 8K, and 16K all reside in suitcase ID 0 while the data table indices are 1, 2, and 3. The lname field 407 is NULL in the filemap because each segment has not previously been referenced by any file.

FIG. 4B illustrates one example of a datastore suitcase corresponding to the filemap file X 401. According to various embodiments, datastore suitcase 471 includes an index portion and a data portion. The index section includes indices 453, data offsets 455, and data reference counts 457. The data section includes indices 453, data 461, and last file references 463. According to various embodiments, arranging a data table 451 in this manner allows a system to perform a bulk read of the index portion to obtain offset data to allow parallel reads of large amounts of data in the data section.

According to various embodiments, datastore suitcase 471 includes three offset, reference count pairs which map to the data segments of the filemap file X 401. In the index portion, index 1 corresponding to data in offset-data A has been referenced once. Index 2 corresponding to data in offset-data B has been referenced once. Index 3 corresponding to data in offset-data C has been referenced once. In the data portion, index 1 includes data A and a reference to File X 401 which was last to place a reference on the data A. Index 2 includes data B and a reference to File X 401 which was last to place a reference on the data B. Index 3 includes data C and a reference to File X 401 which was last to place a reference on the data C.

According to various embodiments, the dictionary is a key for the deduplication system. The dictionary is used to identify duplicate data segments and point to the location of the data segment. When numerous small data segments exist in a system, the size of a dictionary can become inefficiently large. Furthermore, when multiple optimizer nodes are working on the same data set they will each create their own dictionary. This approach can lead to suboptimal deduplication since a first node may have already identified a redundant data segment but a second node is not yet aware of it because the dictionary is not shared between the two nodes. Thus, the second node stores the same data segment as an original segment. Sharing the entire dictionary would be possible with a locking mechanism and a mechanism for coalescing updates from multiple nodes. However, such mechanisms can be complicated and adversely impact performance.

Consequently, a work partitioning scheme can be applied based on segment ID or hash value ranges for various data segments. Ranges of hash values are assigned to different nodes within the cluster. If a node is processing a data segment which has a hash value which maps to another node, it will contact the other node that owns the range to find out if the data segments already exist in a datastore.

FIG. 5 illustrates multiple dictionaries assigned to different segment ID or hash ranges. Although hash ranges are described, it should be recognized that the dictionary index can be hash ranges, reference values, or other types of keys. According to various embodiments, the hash values are SHA1 hash values. In particular embodiments, dictionary 501 is used by a first node and includes hash ranges from 0x0000 0000 0000 0000-0x0000 0000 FFFF FFFF. Dictionary 551 is used by a second node and includes hash ranges from 0x0000 0001 0000 0000-0x0000 0001 FFFF FFFF. Hash values 511 within the range for dictionary 501 are represented by symbols a, b, and c for simplicity. Hash values 561 within the range for dictionary 551 are represented by symbols i, j, and k for simplicity. According to various embodiments, each hash value in dictionary 501 is mapped to a particular storage location 521 such as location 523, 525, or 527. Each hash value in dictionary 551 is mapped to a particular storage location 571 such as location 573, 575, and 577.

Having numerous small segments increases the likelihood that duplicates will be found. However, having numerous small segments decreases the efficiency of using the dictionary itself as well as the efficiency of using associated filemaps and datastore suitcases.

FIG. 6A illustrates one example of a non-container file. According to various embodiments, container files such as ZIP files, archives, productivity suite documents such as .docx, .xlsx, etc., include multiple objects of different types. Non-container files such as images and simple text files typically do not contain disparate objects.

According to various embodiments, it is recognized that certain types of non-container files do not benefit from having a segment size smaller than the size of the file itself. For example, many image files such as .jpg and .tiff files do not have many segments in common with other .jpg and .tiff files. Consequently, selecting small segments for such file types is inefficient. Consequently, the segment boundaries for an image file may be the boundaries for the file itself. For example, noncontainer data 601 includes file 603 of a type that does not benefit from finer grain segmentation. File types that do not benefit from finer grain segmentation include image files such as .jpg, .png, .gif, and .bmp files. Consequently, file 603 is provided with a single segment 605. A single segment is maintained in the deduplication dictionary. Providing a single large segment encompassing an entire file can also make compression of the segment more efficient. According to various embodiments, multiple segments encompassing multiple files of the same type are compressed at the same time. In particular embodiments, only segments having data from the same type of file are compressed using a single compression context. It is recognized that specialized compressors may be applied to particular segments associated with the same file type.

FIG. 6B illustrates one example of a container file having multiple disparate objects. Data 651 includes a container file that does benefit from more intelligent segmentation. According to various embodiments, segmentation can be performed intelligently while allowing compression of multiple segments using a single compression context. Segmentation can be implemented in an intelligent manner for deduplication while improving compression efficiency. Instead of selecting a single segment size or using a sliding segment window, file 653 is delayered to extract file components. For example, a .docx file may include text, images, as well as other container files. For example, file 653 may include components 655, 659, and 663. Component 655 may be a component that does not benefit from finer grain segmentation and consequently includes only segment 657. Similarly, component 659 also includes a single segment 661. By contrast, component 663 is actually an embedded container file 663 that includes not only data that does benefit from additional segmentation but also includes another component 673. For example, data 665 may include text. According to various embodiments, the segment size for text may be a predetermined size or a dynamic or tunable size. In particular embodiments, text is separated into equal sized segments 667, 669, and 671. Consequently, data may also include a non-text object 673 that is provided with segment boundaries aligned with the object boundaries 675.

A variety of devices and applications can implement particular examples of network efficient deduplication. FIG. 7 illustrates one example of a computer system. According to particular example embodiments, a system 700 suitable for implementing particular embodiments of the present invention includes a processor 701, a memory 703, an interface 711, and a bus 715 (e.g., a PCI bus). When acting under the control of appropriate software or firmware, the processor 701 is responsible for such tasks such as optimization. Various specially configured devices can also be used in place of a processor 701 or in addition to processor 701. The complete implementation can also be done in custom hardware. The interface 711 is typically configured to send and receive data packets or data segments over a network. Particular examples of interfaces the device supports include Ethernet interfaces, frame relay interfaces, cable interfaces, DSL interfaces, token ring interfaces, and the like.

In addition, various very high-speed interfaces may be provided such as fast Ethernet interfaces, Gigabit Ethernet interfaces, ATM interfaces, HSSI interfaces, POS interfaces, FDDI interfaces and the like. Generally, these interfaces may include ports appropriate for communication with the appropriate media. In some cases, they may also include an independent processor and, in some instances, volatile RAM. The independent processors may control such communications intensive tasks as packet switching, media control and management.

According to particular example embodiments, the system 700 uses memory 703 to store data and program instructions and maintained a local side cache. The program instructions may control the operation of an operating system and/or one or more applications, for example. The memory or memories may also be configured to store received metadata and batch requested metadata.

Because such information and program instructions may be employed to implement the systems/methods described herein, the present invention relates to tangible, machine readable media that include program instructions, state information, etc. for performing various operations described herein. Examples of machine-readable media include hard disks, floppy disks, magnetic tape, optical media such as CD-ROM disks and DVDs; magneto-optical media such as optical disks, and hardware devices that are specially configured to store and perform program instructions, such as read-only memory devices (ROM) and programmable read-only memory devices (PROMs). Examples of program instructions include both machine code, such as produced by a compiler, and files containing higher level code that may be executed by the computer using an interpreter.

Although many of the components and processes are described above in the singular for convenience, it will be appreciated by one of skill in the art that multiple components and repeated processes can also be used to practice the techniques of the present invention.

While the invention has been particularly shown and described with reference to specific embodiments thereof, it will be understood by those skilled in the art that changes in the form and details of the disclosed embodiments may be made without departing from the spirit or scope of the invention. It is therefore intended that the invention be interpreted to include all variations and equivalents that fall within the true spirit and scope of the present invention. 

What is claimed is:
 1. A method, comprising: monitoring data access requests for optimized data maintained on a plurality of nodes in a cluster, wherein the optimized data comprises deduplicated data; detecting a optimized data storage imbalance; generating a plurality of new keys associated with a mapping function, the mapping function identifying a particular node corresponding to a particular key, wherein each of the plurality of new keys includes a node number, wherein the plurality of new keys correspond to a plurality of blockmap files, wherein each blockmap file includes offset, length, and location identifiers for identifying segments in a plurality of suitcases, each suitcase identifying the location of the segments on disk, wherein the plurality of blockmap files remain unchanged after redistributing optimized data; redistributing optimized data across the plurality of nodes in the cluster, wherein redistributing the optimized data involves updating one or more of the suitcases to modify one or more of the locations of the segments on disk.
 2. The method of claim 1, wherein the plurality of new keys are a plurality of suitcase identifiers (scids).
 3. The method of claim 2, wherein the mapping function is used to identify a particular node and comprises the following: #define get_the_node_number_from_the_scid(_scid_) scid_to_node_array[_scid_(—) % MAX_CLUSTER_SIZE].
 4. The method of claim 1, wherein the data imbalance is a disproportionate rate of data access at a particular node.
 5. The method of claim 1, wherein the data imbalance corresponds to overuse of particular nodes and underuse of other nodes.
 6. The method of claim 1, wherein a plurality of segments are redistributed across the plurality of nodes.
 7. The method of claim 1, wherein the mapping function can be changed while the plurality of new keys are being generated.
 8. A system, comprising: an interface configured to monitor data access requests for optimized data maintained on a plurality of nodes in a cluster, wherein the optimized data comprises deduplicated data; a processor configured to detect an optimized data storage imbalance and generate a plurality of new keys associated with a mapping function, the mapping function identifying a particular node corresponding to a particular key, wherein each of the plurality of new keys includes a node number, wherein the plurality of new keys correspond to a plurality of blockmap files, wherein each blockmap file includes offset, length, and location identifiers for identifying segments in a plurality of suitcases, wherein the plurality of blockmap files remain unchanged after redistributing optimized data; wherein optimized data is redistributed across the plurality of nodes in the cluster, wherein redistributing the optimized data involves updating one or more of the suitcases to modify one or more of the locations of the segments on disk.
 9. The system of claim 8, wherein the plurality of new keys are a plurality of suitcase identifiers (scids).
 10. The method of claim 9, wherein the mapping function is used to identify a particular node and comprises the following: #define get_the_node_number_from_the_scid(_scid_) scid_to_node_array[_scid_% MAX_CLUSTER_SIZE].
 11. The system of claim 8, wherein the data imbalance is a disproportionate rate of data access at a particular node.
 12. The system of claim 8, wherein the data imbalance corresponds to overuse of particular nodes and underuse of other nodes.
 13. An apparatus, comprising: means for monitoring data access requests for optimized data maintained on a plurality of nodes in a cluster, wherein the optimized data comprises deduplicated data; means for detecting a optimized data storage imbalance; means for generating a plurality of new keys associated with a mapping function, the mapping function identifying a particular node corresponding to a particular key, wherein each of the plurality of new keys includes a node number, wherein the plurality of new keys correspond to a plurality of blockmap files, wherein each blockmap file includes offset, length, and location identifiers for identifying segments in a plurality of suitcases, wherein the plurality of blockmap files remain unchanged after redistributing optimized data; means for redistributing optimized data across the plurality of nodes in the cluster, wherein redistributing the optimized data involves updating one or more of the suitcases to modify one or more of the locations of the segments on disk. 